Investigation into pre-determining factors for bubbly bark outbreaks in chestnut orchards (CH05001)

This is a final research report from Hort Innovation’s historical archives. Please note that as these reports may date back as far as the 1990s, the content and recommendations within them may be superseded by more recent research.

What was it all about?

The cause of the chestnut condition known as "Bubbly Bark" was uncertain at the time, although the Chestnut Growers of Australia (CGA) felt that a recent study had narrowed the possibilities.

Bubbly Bark in chestnuts had caused the death of hundreds of young chestnut trees in recent years. It was wide spread in north east Victoria, but also known in southern and northern New South Wales. The condition was very common in Chile and it was also known in New Zealand and the USA.

The early symptoms were a bubbling of the bark in late winter/early spring, often followed by a weak bud burst. Some trees were able to recover during the growing season, while many died. In some orchards the death rate reached nearly 50 per cent, but in others it would only be 1-2 per cent. Until the trees recovered chestnut yield was reduced.

In a study jointly funded by Hort Innovation (which was then Horticulture Australia Limited) and the CGA a number of orchards were monitored during the 2005/2006 growing season. Sites in Wandiligong, Eurobin, Beechworth and Stanley were included in the study. Plantation Development Services Pty Ltd from Bright was engaged by the CGA for the study, as well as two scientists from New Zealand who had previous experience with Bubbly Bark.

The affected trees were almost always young, grafted trees that usually only died above the graft. Seedling or non-grafted trees were seldom affected. Trees that reshooted and grew from below the graft grew healthily for many years. No pathogens were identified in affected trees, despite intensive testing. The levels of calcium and potassium, and possibly magnesium, manganese and aluminium may have influenced the presence of Bubbly Bark.

It appeared that very wet, mild July-October periods caused a reaction in the tree that produced the bubbling of the bark. The process which caused the bubbly effect was unknown, but it may have been associated with the graft union of the tree. As yet, there was limited evidence available to support a particular hypothesis. If the tree was strong enough or the conditions improved the tree had the potential to regain strong vigour, but many trees died.

It was recommended that future efforts included identifying which varieties were more resistant to Bubbly Bark, which varieties were best suited as rootstock, and testing the theory that the graft union was a major factor in the cause of Bubbly Bark. However the search for a pathogen needed to be continued, as did the research into the role of nutrition.